Pyoderma gangrenosum (pie-oh-DER-muh gang-ruh-NO-sum) is a rare condition that causes large, painful sores (ulcers) to develop on your skin, most often on your legs.

It's not certain what causes pyoderma gangrenosum, but it appears to be a disorder of the immune system. People who have certain underlying conditions, such as inflammatory bowel disease or rheumatoid arthritis, are at higher risk of pyoderma gangrenosum.

Treatment typically includes high doses of corticosteroids, such as prednisone, along with other drugs designed to suppress your immune system. It can take weeks or even months to heal the ulcers associated with pyoderma gangrenosum.

Pyoderma gangrenosum usually starts with a small, red bump on your skin, which may resemble a spider bite. Within days, this bump can develop into a large, painful open sore. The ulcers usually appear on your legs, but may develop anywhere on your body. If you have several ulcers, they may grow and merge into one larger ulcer.

When to see a doctor

Talk to your doctor if you develop unexplained blistering on your skin, an itchy rash or a sore that's slow to heal.

The cause of pyoderma gangrenosum isn't well understood. It's often associated with inflammatory conditions, such as ulcerative colitis and Crohn's disease. If you have pyoderma gangrenosum, new skin trauma, such as a cut or puncture wound, may result in the formation of new ulcers. This tendency of new ulcers to form from trauma, including surgery, is known as pathergy.

Pyoderma gangrenosum is most common in people in their 40s and 50s, but can occur at any age. It's also associated with inflammatory conditions, including:

Ulcerative colitis. This disease of the large intestine causes chronic inflammation of your large intestine.

Rheumatoid arthritis. Rheumatoid arthritis refers to a condition in which the thin membranes surrounding your joints become irritated and inflamed.

The ulcers associated with pyoderma gangrenosum often leave scars.

You're likely to start by seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, you may be referred immediately to a doctor who specializes in treating skin conditions (dermatologist).

What you can do

Before your appointment, you may want to write a list that answers some of the following questions:

When did your symptoms begin?

Have you had similar symptoms in the past? If so, what treatment worked then?

What medications and supplements do you take regularly?

What to expect from your doctor

Your doctor is likely to ask you a number of questions, including:

Did you have any damage to your skin, such as a puncture or cut, in the area where the sore developed?

What treatments have you tried already? Have they helped any?

Do you have any inflammatory medical conditions, such as Crohn's disease, ulcerative colitis or rheumatoid arthritis?

There's no test that can specifically confirm a diagnosis of pyoderma gangrenosum. But your doctor may order a variety of tests to rule out other conditions that may have similar signs or symptoms.

Blood tests

A sample of your blood can be tested to check for:

Evidence of infection

Liver, kidney and thyroid function

Rheumatoid factor, which indicates rheumatoid arthritis

Swabs and biopsies

A cotton swab can remove a small sample of liquid from the center of an ulcer to test for different types of infection. A skin biopsy involves removing a small sample of the affected skin, so it can be viewed under a microscope.

Depending on the size and depth of your skin lesions, it can take weeks or months for them to heal. Follow your doctor's instructions carefully regarding wound care. This is especially important because many of the oral medications prescribed for pyoderma gangrenosum suppress your immune system, which increases your risk of infection.

Medications

High doses of corticosteroids, such as prednisone, are the mainstay of pyoderma gangrenosum treatment. Side effects can include thinning bones, weight gain and increased risk of infection. To reduce the amount of prednisone needed, your doctor might recommend that you also take anti-rejection drugs, such as cyclosporine, or medications used more commonly for rheumatoid arthritis.

Surgery

In most cases, surgery isn't a good treatment option because trauma to the skin may worsen existing ulcers or stimulate new ones to develop. But if the ulcers on your skin are large and need help with healing, your doctor might suggest a skin graft — a procedure that surgically attaches a piece of real or artificial skin over the open sores. This is attempted only after the wound inflammation has gone and the ulcer has started healing.

With treatment, you're likely to recover from pyoderma gangrenosum. However, you may feel stress about the possibility of recurrence or about how your skin looks. You may want to talk to a counselor or medical social worker. Or you may find it helpful to talk to other people who have pyoderma gangrenosum.

You can't totally prevent pyoderma gangrenosum. If you have the condition, try to avoid injuring your skin. Injury or trauma to your skin can provoke new ulcers to form. Although not entirely effective, control of any underlying condition that may be causing the ulcers may be of help.

Experience. Pyoderma gangrenosum was first identified by Mayo doctors more than 80 years ago. Although this is a rare disease, Mayo has a long experience in diagnosing and treating it.

Accurate diagnosis. Similar-appearing ulcers can be caused by many diseases. Mayo Clinic specialists work as an integrated team to arrive at an accurate diagnosis so that you get proper treatment.

Comprehensive resources. At each campus, Mayo has the expertise to treat pyoderma gangrenosum and any other disease that may be associated with it.

At Mayo Clinic, we assemble a team of specialists who take the time to listen and thoroughly understand your health issues and concerns. We tailor the care you receive to your personal health care needs. You can trust our specialists to collaborate and offer you the best possible outcomes, safety and service.

Mayo Clinic is a not-for-profit medical institution that reinvests all earnings into improving medical practice, research and education. We're constantly involved in innovation and medical research, finding solutions to improve your care and quality of life. Your doctor or someone on your medical team is likely involved in research related to your condition.

Our patients tell us that the quality of their interactions, our attention to detail and the efficiency of their visits mean health care — and trusted answers — like they've never experienced.

Specialists in dermatology usually manage the care of adults who have pyoderma gangrenosum. Other specialists are involved as needed.

For appointments or more information, call the Central Appointment Office at 800-446-2279 (toll-free) 8 a.m. to 5 p.m. Mountain Standard Time, Monday through Friday or complete an online appointment request form.

Pyoderma gangrenosum was identified by Mayo Clinic dermatologists in 1930. More recently, Mayo clinicians contributed research describing the extent to which pyoderma gangrenosum is misdiagnosed and the types of treatment that work best for the condition.

Mayo publications

See a list of publications by Mayo Clinic doctors on pyoderma gangrenosum on PubMed, a service of the National Library of Medicine.

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